1. Field of the Invention
The present invention relates to a communications device, and more particularly, to a noise reducing apparatus for minimizing spurious noise in a system utilizing a cable modem. The present application is based upon Korean Application No. 99-19223, which is incorporated herein by reference.
2. Description of the Related Art
One of the most important problems in conventional cable modems is the interference between cable modems caused by spurious noise. Spurious noise results in a large amount of ingress noise in the upstream transmission of a cable TV network, thereby adversely affecting communication between the terminal of a cable modem and a headend.
FIG. 1 is a block diagram showing the configuration of a conventional noise reducing apparatus. In a conventional noise reducing apparatus, a central processing unit (CPU) 11 controls the level of upstream transmission through a programmable gain controller 12. The on-off state of the programmable gain controller 12 is controlled by an enable signal of the CPU 11. A transformer 13 transforms the controlled transmission level which is then filtered by a low pass filter (LPF) 14 and tuned by a tuner 15 to be coupled to a coaxial cable network. The conventional cable modem has a disadvantage in that it cannot turn off the enable signal completely nor exclude all the radio frequency even if it can turn off the enable signal completely, when the cable modem does not transmit a signal. This results in the generation of spurious noise, which restricts smooth communication.
To solve the above problem, it is an objective of the present invention to provide a noise reducing apparatus for minimizing spurious noise when a cable modem does not transmit a signal, in which a circuit formed of gallium arsenide (GaAs) integrated circuit (IC) single pole double throw (SPDT) switches is used.
Accordingly, to achieve the above objective, it is preferable that a noise reducing apparatus for reducing noise generated in the operation of a modem includes a controlling unit for controlling the modem and producing an enable signal according to the presence of the noise, a gain controller for controlling the on-off state of a transmission level in response to the enable signal of the controlling unit, a noise removing unit for removing predetermined noise generated by the transmission level of the gain controller when the cable modem does not transmit a signal, and a tuner for tuning the output of the noise removing unit to connect it to a coaxial cable network.